1. Field of the Invention
The present invention relates generally to wireless systems, and more specifically to reliable packet detection in a wireless receiver when packets contain a known repetitive sequence.
2. Related Art
A wireless receiver receives packets (communication/data) over a wireless medium. Wireless communication is often performed in an asynchronous fashion, wherein the specific time instances of transmission of packets may not be known apriori. Therefore, a wireless receiver may check the wireless medium for the presence of a valid packet (i.e., perform packet detection), and performs further processing (such as decoding the data in the packet) upon detection of a valid packet. Since interference (generally any signal other than a desired signal) may also be present in the wireless medium it is desirable that packets be detected in a reliable manner even in the presence of such interference.
Packets may be designed to contain known repetitive sequences to aid a wireless receiver in packet detection. For example, packets transmitted according to the 802.11a/g standard contain repeated sequences (known to a potential receiver) in a preamble/header portion at the start of a packet.
A prior wireless receiver performs packet detection by cross correlating a locally stored (in the wireless receiver) preamble with a signal (potentially) present in the wireless medium. Cross correlation entails finding similarity between the local preamble and the received continuous signal starting at different time instances. When the compared signal in the wireless medium represents a preamble contained in a valid packet, a cross-correlation operation produces a result with a large value.
Thus, upon producing a large value, the compared signal is deemed to represent (a specific portion of) the preamble, and the packet is deemed to be detected. The signal portion (in the continuous signal) representing the packet is determined in relation to the compared signal. In particular, the portion following the preamble may be deemed to contain the rest of the packet of interest.
However, the cross correlation operation may also produce a similarly large valued result when the signal in the wireless medium is an interference signal, thereby reducing the reliability of the packet detection operation. The resulting false detections may be undesirable for several reasons, such as reduced effective transmission throughput (as the device may decide not to transmit in view of the ‘reception’ of packets), unneeded power consumption due to processing of packets, etc.
It is thus generally desirable that packets on a wireless network be reliably detected.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.